In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions of the resist film become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material that satisfies these conditions, a chemically amplified resist composition is used, which includes a base component that exhibits changed solubility in a developing solution under the action of acid, and an acid generator component that generates acid upon exposure. For example, in the case where the developing solution is an alkali developing solution (alkali developing process), a positive-type chemically amplified resist composition containing a resin component (base resin) that exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator component is generally used. If a resist film formed using this resist composition is selectively exposed during formation of a resist pattern, then acid is generated from the acid generator component within the exposed portions, and the action of this acid causes an increase in the solubility of the base resin in an alkali developing solution, making the exposed portions soluble in the alkali developing solution. Accordingly, by performing alkali developing, the unexposed portions remain as a pattern, resulting in the formation of a positive-type pattern.
The base resin used exhibits increased polarity under the action of acid, thereby exhibiting increased solubility in an alkali developing solution, whereas the solubility in an organic solvent is decreased. Accordingly, if a solvent developing process that uses a developing solution containing an organic solvent (an organic developing solution) is employed instead of an alkali developing process, then within the exposed portions of the resist film, the solubility in the organic developing solution decreases relatively, meaning that during the solvent developing process, the unexposed portions of the resist film are dissolved in the organic developing solution and removed, whereas the exposed portions remain as a pattern, resulting in the formation of a negative-type resist pattern. This type of solvent developing process that results in the formation of a negative-type resist pattern is also referred to as a negative-type development process (for example, see Patent Document 1).
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are generally used as base resins for chemically amplified resist compositions that use ArF excimer laser lithography or the like, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 2).
Here, the term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position. The term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position.
Further, as acid generators usable in a chemically amplified resist composition, various types have been proposed including, for example, onium salt acid generators, oxime sulfonate acid generators, diazomethane acid generators, nitrobenzylsulfonate acid generators, iminosulfonate acid generators, and disulfone acid generators.
Resins having an acid-generating group that generates acid upon exposure have also been proposed as base resins for chemically amplified resist compositions. For example, in order to achieve high resolution and the like, resin components that have, within the resin structure, an acid-generating group that generates acid upon exposure, and an acid-decomposable group that exhibits changed polarity under the action of acid have been proposed (for example, see Patent Documents 3 and 4). These resin components combine the function of an acid generator and the function of a base resin, and enable a chemically amplified resist composition to be formed from a single component. In other words, when this type of resin component is subjected to exposure, acid is generated from the acid-generating group within the structure, and the action of that acid causes decomposition of the acid-decomposable group, thereby forming a polar group such as a carboxyl group that causes an increase in the polarity. As a result, when a resin film (resist film) formed using this resin component is subjected to selective exposure, the polarity of the exposed portions increases, and by performing developing using an alkali developing solution, the exposed portions can be dissolved and removed, forming a positive-type resist pattern.
In recent years, investigations have been conducted into the use of extreme ultraviolet rays (EUV) electron beams (EB) and X-rays, which have a shorter wavelength (and higher energy) than an ArF excimer laser.
Resist materials for use in EUV lithography and EB lithography require specific lithography properties, including sensitivity to EUV or EB, and a high resolution capable of forming the targeted very fine resist patterns, and also require a favorable resist pattern shape.
Currently, chemically amplified resists that have been proposed for use with KrF excimer lasers or ArF excimer lasers or the like are generally used as the resist materials for EUV lithography and EB lithography due to their superior lithography properties.
Chemically amplified resists containing an acrylic resin as the base resin are considered to have particularly superior lithography properties.